1. Field of the Invention
The present invention relates generally to flat panel display devices and methods of fabricating the same and, more particularly, to an organic electroluminescent display (OLED) device having a protective layer that may provide superior resistance to moisture and oxygen infiltration, and to a method of manufacturing the same.
2. Description of Related Art
Flat panel displays may be categorized as emission devices or as non-emission devices. Examples of emission devices are a flat cathode ray tube (CRT), a plasma display panel, an electroluminescent device, and a light emitting diode. An example of a non-emission device is a liquid crystal display (LCD). Of these display devices, electroluminescent devices have wider viewing angles, faster video response speeds, and lower power consumption than the conventional CRT displays. Other advantages over CRTs include increased brightness, lighter weight, improved durability, and expanded ranges of operating temperatures. OLEDs may be classified as organic or inorganic depending on the type of material that forms the OLEDs' emission layer. For these and other reasons, OLEDs are considered to be next-generation replacements of CRT displays.
An OLED device includes an emission layer composed of an organic compound that is sandwiched between an anode and a cathode. When voltages are applied to the anode and cathode, holes from the anode migrate, via a hole transport layer, to an emission layer. Electrons from the cathode migrate, via an electron hole transport layer (ETL), to the emission layer, in which the electrons and holes recombine to generate exitons. As the exitons fall from their excited states to a ground state, they cause fluorescent molecules of the emission layer to emit light. Images are formed by selectively switching patterns of unit pixels regions on and off. Full color OLED devices have pixels that emit one of three light colors, namely red (R), green (G), or blue (B).
To ensure a long operating life, the emission layer and the cathode on the emission layer should be shielded from moisture to be protected from oxidation and shielded from oxygen infiltration to be protected from exfoliation. An example of shielding is set forth in Korean Patent Publication No. 2001-0067868, which discloses forming a layer of an insulating polymer compound, such as high density polyethylene, on an emission layer and a metal electrode using a vacuum system; forming a layer of an inorganic metal on the polymer compound layer; forming a layer of an insulating inorganic metal on the inorganic metal layer; and forming a layer of an insulating polymer compound on the insulating inorganic metal layer. Nevertheless, the lifespan of the OLED taught by the Korean Patent Publication No. 2001-0067868 does not reach satisfactory levels and offers poor light extraction efficiency, and thus improvement is needed.